1. Field of the Invention
This invention relates to articles prepared from novel anionic block copolymers of aromatic vinyl compounds and conjugated dienes, and to blends of such block copolymers with other polymers. The invention also relates to formed articles and methods for forming articles from such novel block copolymers.
2. Background of the Art
The preparation of block copolymers of mono alkenyl arenes and conjugated dienes is well known. One of the first patents on linear ABA block copolymers made with styrene and butadiene is U.S. Pat. 3,149,182. Over the last forty plus years a large number of new styrene diene polymers have been developed. Such polymers include linear polymers, radial polymers, asymmetric polymers, hydrogenated polymers, functionalized polymers and the like. In most cases the polymer was developed to meet an important customer need that was not currently being met. This has been a very dynamic process, and has resulted in enormous growth for new styrene/diene block copolymers and new uses to meet consumer demands.
Even with the growth of many new polymers, there still are consumer demands that go unfulfilled. For example, it has long been desired to have a polymer with high molecular weight in conjunction with easy processability. High molecular weight polystyrene blocks are often necessary to achieve good high temperature performance particularly in automotive applications. In order to maintain a constant polystyrene content, an increase in the polystyrene block molecular weights forces an increase in the total polymer molecular weight. This leads to very high viscosities and often intractable flow. In order to achieve the high molecular weights desired, at acceptable processing conditions, a new polymer has been discovered. This new polymer is an A1-B1-A2-B2 tetrablock copolymer, having particular molecular weights and structure. What has now been found is that blends or compounds of these novel tetrablock copolymers with processing oils and other polymers have surprising property advantages, and show promising utility in a variety of end-use applications, including injection molding, extruded goods and polymer modification. The polymers of the present invention allow for improved processability at high molecular weights analogous to those of block copolymers currently available in the market. This is observed through improvements in compound melt flow without a reduction in properties at elevated temperature.